| 摘要 |
PURPOSE:To eliminate the logic gate of a polarity inversion control part by inverting the polarity of only a transmission data line, held in a space state in power feed, only during the 1st data link establishment, by using a function of transmitting and receiving a length mark and length space. CONSTITUTION:In power feed, the output of bit holding circuit 2 is held at logic ''1'' and that of polarity inversion control circuit 3 at logic ''0''. Therefore, the output of AND gate 20 is at logic ''0'' and that of transmitting circuit 5 has the space polarity. After the power feed, the output of polarity inversion control circuit 3 is changed from logic ''0'' to ''1''. Consequently, the output of AND gate 20 has logic ''1'', and that of transmitting circuit 5 has the mark polarity. On the other hand, when a terminal side detects the polarity inversion of the center side, the polarity of reception data line 15 at the center side is inverted. The center detects a long mark to set up a data link. On the completion of data from the center, long space transmission is carried out via transmission data line 16. |
